Exploring the Burro Mesa Locale, Part 1: Layer-Cake Geology | Big Bend National Park, Texas, USA
Facing northeastward. We're just a little northeast of the Burro Spring Trailhead.
Geologists, including this one, are forever likening sequences of sedimentary strata, or for that matter layers of igneous extrusive rocks, to layer cakes. But here we have a nice succession of volcanic and sedimentary deposits that in aggregate actually looks like one. It's not difficult to imagine gigantic birthday candles on top of it.
This is Burro Mesa, one of Big Bend's most notable and petrologically and stratigraphically educative landforms. As I write this, I am feeling the uncontrollable urge to do another one of my kindergarten-level diagrams with colored lines and numbers. I'll post that as Part 2 in this new set.
In the meantime, see if you can visualize the following sequence:
- The Rhyolite Member of the Burro Mesa Formation (Oligocene in age), providing the resistant cap on top.
- Just below it, the Wasp Spring Member of the Burro Mesa Formation (Oligocene), consisting of the very prominent and vertically jointed section of cliffs composed of tuffs, surge deposits, and suchlike.
- Extensive Quaternary colluvium deposits and one lovely colluvial fan (the pyramidal, ramp-like feature at left). These largely blanket a younger portion of the Chisos Formation (Oligocene). However, some of the latter is sticking out visibly at middle. One source describes it as a volcanically derived conglomerate.
- At bottom of the cake, sticking out prominently at lower right, are black, bedlike flows of the Bee Mountain Basalt Member of the Chisos Formation (yes, it too is Oligocene). We'll get a very close look at that basalt in later photos of this set.
Note that this sequence is essentially the same as that of Cerro Castellan, though there older Chisos Formation tuff underlying the Bee Mountain Basalt is also visible.
To see the other photos and descriptions in this set and my other Big Bend series, visit my my Exploring the Burro Mesa Locale album.
Exploring the Burro Mesa Locale, Part 1: Layer-Cake Geology | Big Bend National Park, Texas, USA
Facing northeastward. We're just a little northeast of the Burro Spring Trailhead.
Geologists, including this one, are forever likening sequences of sedimentary strata, or for that matter layers of igneous extrusive rocks, to layer cakes. But here we have a nice succession of volcanic and sedimentary deposits that in aggregate actually looks like one. It's not difficult to imagine gigantic birthday candles on top of it.
This is Burro Mesa, one of Big Bend's most notable and petrologically and stratigraphically educative landforms. As I write this, I am feeling the uncontrollable urge to do another one of my kindergarten-level diagrams with colored lines and numbers. I'll post that as Part 2 in this new set.
In the meantime, see if you can visualize the following sequence:
- The Rhyolite Member of the Burro Mesa Formation (Oligocene in age), providing the resistant cap on top.
- Just below it, the Wasp Spring Member of the Burro Mesa Formation (Oligocene), consisting of the very prominent and vertically jointed section of cliffs composed of tuffs, surge deposits, and suchlike.
- Extensive Quaternary colluvium deposits and one lovely colluvial fan (the pyramidal, ramp-like feature at left). These largely blanket a younger portion of the Chisos Formation (Oligocene). However, some of the latter is sticking out visibly at middle. One source describes it as a volcanically derived conglomerate.
- At bottom of the cake, sticking out prominently at lower right, are black, bedlike flows of the Bee Mountain Basalt Member of the Chisos Formation (yes, it too is Oligocene). We'll get a very close look at that basalt in later photos of this set.
Note that this sequence is essentially the same as that of Cerro Castellan, though there older Chisos Formation tuff underlying the Bee Mountain Basalt is also visible.
To see the other photos and descriptions in this set and my other Big Bend series, visit my my Exploring the Burro Mesa Locale album.